Transfer sheet peeling device for xerographic apparatus

ABSTRACT

Apparatus to remove the copy sheet from the photoconductive surface of a xerographic machine following transfer of the image thereto. The apparatus consists of a pressure manifold having at least one discharge orifice directed toward a separation point on the photoconductive surface downstream of the transfer station, a source of pressure air, a valve to regulate the admission of pressure air to the manifold, and control means to actuate the valve as the leading edge of the copy sheet approaches the separation point. To obtain accurate response, a photocell type sheet detector is used to detect the leading edge of the copy sheet.

United States Patent Suda [54] TRANSFER SHEET PEELI NG DEVICE FOR XEROGRAPHIC APPARATUS [721 Inventor: Katsuhide Suda, lchikawa, Japan [73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: May 10,1971

[21] Appl. No.: 141,915

[30] Foreign Application. Priority Data 3/1963 Hajos ..27l/74 6/1968 Turner ..27l/74 Primary Examiner-Evon C. Blunlc Assistant Examiner- Bruce H. Stoner, Jr.

Attorney-James J. Ral'abate, Donald F. Daley and Frederick E. McMullen [5 7] ABSTRACT Apparatus to remove the copy sheet from the photoconductive surface of a xerographic machine following transfer of the image thereto. The apparatus consists of a pressure manifold having at least one discharge orifice directed toward a separation point on the photoconductive surface downstream of the transfer station, a source of pressure air, a valve to regulate the admission of pressure air to the manifold,

and control means to actuate the valve as the leading edge of the copy sheet approaches the separation point. To obtain accurate response, a photocell type sheet detector is used to detect the leading edge of the copy sheet.

1 Claim, 4 Drawing Figures PATENTEDBEH 5 i912 3.704.881

SHEET 1 BF 3 FIG:

INVENTOR KATSUHIDE SUDA ATTORNEY PAIENT'EDBEC M2 3.704.881

SHEET 2 BF 3 VII/ll,

PATENT'EDBEB 1912 3.704.881

SHEET 3 OF 3 This invention relates to an improvement on the transfer sheet peeling device which assuredly peels off the transfer sheet from the photosensitive drum in a xerographic apparatus.

Recently widely utilized in various fields are xerographic apparatus, which in general consists of the steps of placing an uniform positive or negative electrostatic charge on the photoconductive layer of photosensitive drum by means of corona discharge, projecting a light image of the pattern to be reproduced on the surface of said drum to form an electrostatic latent image thereon, developing the thus formed latent image and the developed toner image onto a transfer sheet. A peeling device which is provided directly after the image transfer position to peel off the front end of the transfer sheet from the surface of said photosensitive drum, peels off said front end and places said end on a conveyor, on which the xerographic toner image on said transfer sheet is fixed permanently.

Such xerographic copying apparatus is characterized by the extremely simple operation required, and the possibilities of very rapid reproduction and of making copies on ordinary paper.

Such copying apparatus is associated, however, with a drawback of so-called paper jamming. The transfer sheet is sometimes not peeled off from the photosensitive drum but rotates with said drum and entangles with the succeeding transfer sheet to cause so-called paper jamming.

Other objects and advantages will be apparent from the ensuing description and drawings in which:

FIG. I is a side-view of internal structure showing an example of xerographic apparatus embodying the present invention;

FIG. 2 is a perspective view of the conventional transfer sheet peeling device;

FIG. 3 is a drawing explaining the function of the transfer sheet peeling device shown in FIG. 2; and

FIG. 4 shows the construction of an example embodying this invention.

In the following the problem of paper jamming will be detailedly explained in reference with the attached drawing. In FIG. 1, the photoconductive surface of photosensitive drum 107 is positively or negatively charged by means of a corona charging device 101, and the original pattern is projected on said charged drum 107 in the direction of arrow 102 to form electrostatic latent image. Said latent image is then subjected to cascade development in a developing device 103 to stick the toner (colored resin powder) on the surface of said photosensitive drum 107 according to the original pattern. Afterwards, the toner is successively transferred from drum 107 to the transfer sheet 108 by giving electrostatic charge to the rear side of said transfer sheet 108 by means of a corona discharge device 104. After said transfer said transfer sheet 108 is peeled off by the front end thereof by means of a peeling device 109 and conveyed by a belt conveyor 110 to the fixing device 105, where the toner image is fixed by melting on said transfer sheet 108.

One type of peeling device 109, which generally consists of the structure as shown in FIGS. 2 and 3 and is provided principally in order to peel off the transfer sheet 108 from said photosensitive drum 107 after transfer of the image, is composed essentially of a manifold 21, compressor 22 and solenoid 23. Com-' pressor 22 is composed of a piston rod 31 provided with a valve piston 37 in cylinder 32, said piston rod 31 being mounted so as to be in contact with the armature 33 of said solenoid 23 and said cylinder. 32 being connected, through a pipe 34, to said manifold 21. Said manifold 21 is mounted at a determined angle with respect to the surface of said photosensitive drum 107, and said armature 33 of the solenoid 23 when activated by electric current pushes said piston rod 31 and piston 37 in said cylinder 32 to bring said piston into the state represented by dotted line in FIG. 3. Consequently the air contained in said cylinder 32 is supplied by the piston 37 and blown from the slit 35 provided on the manifold 21 to separate the front end of the transfer sheet 108 from the surface of the photosensitive drum 107. When the current in the solenoid 23 is interrupted, the armature 33 together with piston 37 and piston rod 31 is brought back to the original position by means of a spring 36. This drawback or return of piston 37 often causes noise. In addition, in the conventional peeling device 109, the piston 37 provided on the piston rod 31 may become worn out or dried in the prolonged use to form a gap at the wall of said cylinder 32. The for mation of such gap decreases the amount of air blown out from the manifold 21 to deteriorate the efficiency of said peeling device, thereby resulting in the rotation of transfer sheet 108 with the photosensitive drum 107 without separation therefrom and leading to the paper jamming.

Such paper jamming is more frequently observed in winter due to decreased humidity in the air and resulting air leakage around the piston 37. Nevertheless, the largest cause for paper jamming is the timing of air blowing from the manifold 21, or namely of function of solenoid 23. In the conventional peeling device 109, the time of peeling is determined bysynchronizing a microswitch to activate said solenoid 23 with the feeding mechanism of said transfer sheet 108, and, therefore, the peeling operation cannot be carried out satisfactorily if the transfer sheet 108 is fed slightly too fast or too slow with respect to the photosensitive drum 107 since the air blowing from the manifold 21 is mislocated with respect to the transfer sheet 108.

Furthermore, even a very slight error in synchronization will cause the air blown from the manifold 21 to be directed on the surface of said photosensitive drum 107 or the surface of said transfer sheet 108 instead of the front end thereof, thereby rendering smooth peeling operation impossible. In fact, the paper jamming arising from such synchronization error is so frequent that the xerographic copying apparatus is ordinarily provided with an automatic switch to interrupt the operation of the apparatus in order to prevent the damage on various parts caused by the jammed paper.

The present invention is accomplished in order to remove such drawback, and is to provide a transfer sheet peeling device for xerographic copying apparatus which detects the exact position where the transfer sheet is to be peeled off from the surface of photosensitive drum and assuredly realizes the peeling thereby preventing the paper jamming.

The construction of the transfer sheet peeling device according to this invention will be explained with reference to an embodiment thereof shown in the attached drawing. In FIG. 4, a compressor 1 driven by means of a motor 2 provides compressed air to an air reservoir 3 and is automatically stopped when the pressure in said reservoir 3 amounts to a determined value. Said reservoir 3 is connected to a manifold through a solenoid valve 4 and air pipe 6. The slit 5a provided on saidmanifold '5 is placed at a position suitable to peel off the transfer sheet 108 sticking on the surface of the photosensitive drum 107, and a light source 9 such as an electric lamp or a potassium-arsenic photo-emitting diode and a photoelectric element 10 such as photoelectric tube or photocell are provided at the position most suitable for such peeling.

Said photoelectric element 10 is connected, through an amplifier 11, with a relay 12, of which output terminals are connected with the terminals of solenoid valve 4.

In this case the parts such as compressor, air reservoir, etc. can be relatively very small and pneumatically connected with air pipes regardless of the actual arrangement in the apparatus.

With such construction, the compressor 1 driven by the motor 2 is automatically stopped when the pressure in the air reservoir 3 reaches a determined value and starts operation again when said pressure is lowered to maintain the internal pressure of said reservoir at a constant value, which can be determined arbitrarily.

When the transfer sheet 108 is not fed or does not reach the point p illuminated with the light source 9, the photoelectric element 10 only receives little light insufficient for activating the relay 12 since the surface of the photosensitive drum 107 is black colored or much darker than the surface transfer sheet 108 and the projected light from the light source 9 is mostly absorbed thereon. When the transfer sheet 108 reaches the point p, however, the photoelectric element receives a stronger reflected light from the surface of i said transfer sheet 108 to generate a relatively large electrical signal, which is amplified and activates the relay l2. Said relay, upon activation, closes the contacts thereof and opens the solenoid valve 4, which allows the passage of compressed air contained in the air reservoir through the slit 5a provided on the manifold 5 to the front end of the transfer sheet thereby peeling off said sheet from the photosensitive drum. The duration of air blow from said manifold 5 can be arbitrarily varied by means of the adjustment of aid relay 12 or of the mechanism of sglenoid valveA, and the pressure of air blow can be varied by changing the internal pressure of said air reservoir 3 so as to obtain the optimum pressure for peeling of the transfer sheet 108.

As thus far explained, the transfer sheet peeling device according to the present invention is characterized by:

the absence of paper jamming resulting from synchronization error, since the peeling is not synchronized with the paper feeding mechanism nor any other mechanism:

the accurate peeling operation enabled by a very short response time from the detection of the transfer sheet to the air blow due to the use of compressed air reservoir as well as of an optical detecting system, in contrast to the time delay between the operation of microswitch and the air blow in conventional peeling devices of the type described herein. This delay cannot be ignored as copying speeds become higher and higher, etc.

the absence of complicated adjustmental work for peeling synchronization, leading to a large economization of labor power:

the absence of troubles resulting from wear or drying out by the conventional pump type compressor:

' a simpler and cheaper mechanism with improved reliability since the paper jamming preventative mechanism can. be dispensed with as the peeling operation is realized assuredly:

the compactness since the components such as compressor, air reservoir, solenoid valve, relay, etc., not only can be relatively small but also can be arranged arbitrarily as the connections therebetween are electhe absence of shock noise which is generated when the armature of solenoid is returned by means of a spring in the conventional peeling device and which is considered inherent to similar devices.

I claim:

1. A transfer sheet peeling device for xerographic apparatus consisting of a light source to project light beam onto a position on the surface of photosensitive drum where the transfer sheet is to be peeled from said surface, a photoelectric element to receive the reflected light of said light beam emitted from said light source, a solenoid valve to be opened by means of the output signal of said photoelectric element, an air reservoir holding compressed air supplied from a compressor at a determined pressure and releasing said compressed air when said solenoid valve is opened, and

a manifold to blow compressed air released from said air reservoir through slit provided thereon thereby detecting optically the front end of the transfer sheet sticking on said photosensitive drum and peeling said sheet from said drum by means of the compressed air blown from said manifold. 

1. A transfer sheet peeling device for xerographic apparatus consisting of a light source to project light beam onto a position on the surface of photosensitive drum where the transfer sheet is to be peeled from said surface, a photoelectric element to receive the reflected light of said light beam emitted from said light source, a solenoid valve to be opened by means of the output signal of said photoelectric element, an air reservoir holding compressed air supplied from a compressor at a determined pressure and releasing said compressed air when said solenoid valve is opened, and a manifold to blow compressed air released from said air reservoir through slit provided thereon thereby detecting optically the front end of the transfer sheet sticking on said photosensitive drum and peeling said sheet from said drum by means of the compressed air blown from said manifold. 